This invention relates generally to medical devices, and more particularly to devices for occluding a vessel of a human or veterinary patient.
Vasoocclusive devices are surgical implants which are placed within the blood vessels or vascular cavities (hereinafter, xe2x80x9cvesselsxe2x80x9d) of a human or veterinary patient. Vasoocclusive devices form an occlusion, thrombus, embolism, blockage or the like in the vessel at the site of implantation. Sites of interest are often the cranial arteries but may be any other site where occlusion is desired.
There are a number of reasons why it may be desirable to occlude a vessel. For example, the site of a stroke or other vascular accident can be treated by placing an occlusive device proximal of the site to block the flow of blood to the site, thereby alleviating leakage at the site. An aneurysm can be treated by the introduction of a vasoocclusive device through the neck of the aneurysm; the thrombogenic nature of the device causes a mass to form in the aneurysm and lowers the potential for growth of the aneurysm and its subsequent rupture. Other diseases, such as tumors and the like, can be treated by occluding the flow of blood to a targeted site of interest.
Several known vasoocclusive devices include a coil having a plurality of fibers, threads, strands or the like (hereinafter, xe2x80x9cfibersxe2x80x9d) extending either laterally of the coil, or connected to and extending along the side of the coil, or extending from an end of the coil. The fibers can be loops or can have free ends. Such devices are typically implanted by the use of a catheter introduced into the bloodstream at a convenient site, often the femoral artery in the groin, and advanced to the site of interest. More particularly, such devices are often supplied in prepackaged form in a sterile cannula which is adapted to engage the proximal end of a catheter. Once the catheter is in place within a vessel of interest, the coil-containing cannula is placed in engagement with the proximal end of the catheter, and the coil is transferred from the cannula and into the catheter by exerting a force on the proximal end of the coil. A pusher rod is then used to push the coil through the catheter to the site at which release of the coil is desired. Typically, the coil is radiopaque, permitting its location to be visualized. Once the coil is at the site of interest, the pusher rod is used to plunge the coil from the catheter and into the vessel. The fibers or fiber loops on the coil extend outwardly from the coil surface to fill the vessel.
While such vasoocclusive devices are generally useful for their intended purpose, their use can be subject to several practical drawbacks. Perhaps most importantly, conventional vasoocclusive devices are often not useful in relatively small vessels such as cranial vessels. More specifically, such prior devices are often useful only in vessels exceeding about 2.7 mm in diameter.
A variety of other objects have been used in an attempt to occlude these smaller vessels. Such other objects have included bits of blood clot, silicone spheres, long or short pieces of wire guide material, polyester (for example, DACRON(copyright)) fibers, silk threads and bits of Gelfoam. All of these have the advantage over coil-type devices in that they can be injected into the vessel of interest through a micro catheter such as the COOK(copyright) MICROFERRET(trademark) (a trademark of Cook Incorporated, Bloomington, Ind.). Saline or a contrast agent is typically used to inject the object through the micro catheter.
While the injection of such objects is advantageous in that the need for a pusher rod (wire guide) is eliminated, their use is subject to practical drawbacks. Most notably, any such object that is small enough to be delivered through a small bore catheter is not large enough to lodge well in the target vessel and form an effective occlusion. While such objects can be injected easily, once they leave the tip of the catheter they continue to travel along the vessel until they reach some sort of restriction in which they can become lodged. The occlusion is then formed wherever such lodging occurs. The physician has to be very careful when injecting such objects to ensure that the occlusion will occur in a useful place. Quite simply, the physician cannot simply expect the occlusion to occur at or near the catheter tip; to the contrary, the physician has little control over where the occluding object will lodge. Unfortunately, the occluding device may travel too far downstream in the vessel, and may even lodge in a place where the device may do more harm than good for the patient.
It would be highly desirable to have a vasoocclusive device whose lodging in a vessel was very reliable and whose positioning could be controlled with great precision. It would also be highly desirable to have such a device which could be used in vessels of very small diameter, in particular, in vessels having a diameter below about 2.7 mm. It would further be highly desirable to have such a device which could be introduced into a patient by injection with a fluid, rather than by being pushed with a rod or the like.
The foregoing problems are solved and a technical advance is achieved in an illustrative vasoocclusive device which is particularly useful in small vessels, preferably in cranial vessels smaller than about 2.7 mm in diameter. Like coil-type devices useful in larger vessels, the device of the present invention comprises a central member and a plurality of fibers or the like extending from the ends of the central member. Advantageously, the member can be significantly smaller than the coils employed in prior coil-type devices. However, the pluralities of fibers on the ends of the member are asymmetric; that is, the fibers on one end of the member are, on average, significantly longer than the fibers on the other end of the member. In particular, the average fiber length on the end of the member which leads the device during its introduction (designated herein as the xe2x80x9cdistalxe2x80x9d end of the member) is only about 20 percent to about 50 percent of the average fiber length on the trailing end of the member (designated herein as the xe2x80x9cproximalxe2x80x9d end of the member). Stated alternatively, the average proximal fiber length is about 2 to about 5 times as great as the average distal fiber length.
This asymmetric arrangement of the fibers on the ends of the central member of the device of the present invention is particularly advantageous in that the device lodges quite well immediately upon expulsion from the catheter, rather than migrating in the vessel before lodging. This reliable lodging gives the physician significantly more confidence about and precise control over the position of the occlusion formed by the device. Of course, unlike the prior coil-type devices, the vasoocclusive device of the present invention can be injected through a micro catheter, obviating the need for a pusher rod or wire guide.
The superior performance of the vasoocclusive device of the present invention appears to result from the asymmetric arrangement of the fibers on the end of the central member. More particularly, it appears that as the device is expelled from the tip of the micro catheter, it is traveling some small amount faster than the blood in the vessel. As a result, the shorter, leading distal fibers tend to spread out and create some drag against the vessel wall. This drag slows the device to a little less than the velocity of the blood. As a result of such slowing, the longer, trailing proximal fibers begin to spread out and bunch up around the central member. The flow of blood increases the pressure on the proximal fibers, and this pressure is transferred by the central member to the distal fibers, causing the distal fibers to bunch up tighter ahead of the member. Such bunching increases the effective cross-sectional area of the device and causes the device to lodge immediately and reliably, and block blood flow through the vessel. Preferably, both the proximal and distal fibers are longer than the central member, facilitating reliable lodging. The improved lodging which results from this xe2x80x9cdrag differentialxe2x80x9d between the shorter distal fibers and the longer proximal fibers is quite pronounced, in contrast to fibers alone, and in contrast to devices having fibers on only one end of a central coil or having fibers of equal length.
In a first aspect, then, the present invention is directed to a vasoocclusive device adapted for introduction into a vessel of a human or veterinary patient and capable of occluding a flow in the vessel when introduced into the vessel, comprising: a member having a proximal end and a distal end spaced from the proximal end, the distal end of the member being introduced into the vessel before the proximal end of the member is introduced into the vessel; a distal plurality of fibers having an average distal fiber length, the distal plurality of fibers being associated with and extending away from the distal end of the member; and a proximal plurality of fibers having an average proximal fiber length, the proximal plurality of fibers being associated with and extending away from the proximal end of the member; wherein the average proximal fiber length is greater than the average distal fiber length.
Preferably, the average proximal fiber length is about two to about five times the average distal fiber length, while both the average distal fiber length and the average proximal fiber length are greater than the length of the member, that is, greater than the distance between the proximal end and the distal end of the member. More preferably, the average distal fiber length is about 4 mm to about 8 mm, and the average proximal fiber length is about 9 mm to about 15 mm. The distal and proximal pluralities of fibers each preferably comprise 8 to 10 individual fibers composed of 40 denier polyester (for example, DACRON(copyright)), nylon or silk.
Also preferably, the member is radiopaque and is cylindrical in shape. The member can be a segment of cannula or plastic tubing. In such a case, the proximal plurality of fibers can be formed continuously with the distal plurality of fibers, and can be secured inside the segment with a medical grade adhesive. Alternatively, the proximal and distal pluralities of fibers can be formed from a plurality of individual fibers joined at a location significantly offset from their centers. The individual fibers can be joined by gluing, knotting or the like; the locus at which they are joined will have an appreciable length (that is, the locus will be at least a few times longer than the diameter of the individual fibers), so that the member comprises the locus of such joining. It is still sensible to refer to the locus of such joining as having proximal and distal ends.
It is preferred, however, that the member is a coil of platinum, stainless steel or tungsten, the coil having a plurality of windings. The distal and proximal pluralities of fibers can then be trapped between the windings of the coil if adjacent windings of the coil abut one another, or can be wrapped about single windings of the coil if adjacent windings of the coil do not abut one another. The length of the member, that is, the distance between its proximal and distal ends, can be about 1.5 mm to about 3.0 mm. The member is preferably no more than about 2.7 mm wide, and more preferably about 0.25 mm to about 0.4 mm wide.
In a second aspect, the present invention is directed to a device of the type disclosed above, comprising a specific combination of the preferred elements disclosed above. More particularly, in this second aspect, the present invention is directed to a vasoocclusive device adapted for introduction into a vessel of a human or veterinary patient and capable of occluding a flow in the vessel when introduced into the vessel, comprising: a radiopaque member having a proximal end and a distal end spaced from the proximal end, the distal end of the member being introduced into the vessel before the proximal end of the member is introduced into the vessel, and the member being about 1.5 mm to about 3.0 mm in length; a distal plurality of fibers having an average distal fiber length, the distal plurality of fibers being associated with and extending away from the distal end of the member; and a proximal plurality of fibers having an average proximal fiber length, the proximal plurality of fibers being associated with and extending away from the proximal end of the member; wherein the average proximal fiber length is about two to about five times the average distal fiber length, the average distal fiber length is about 4 mm to about 8 mm and the average proximal fiber length is about 9 mm to about 15 mm; wherein the average distal fiber length and the average proximal fiber length are both greater than the length of the member; wherein the member comprises a cylindrical coil of platinum, stainless steel or tungsten including a plurality of abutting windings; wherein the distal plurality of fibers comprises 8 to 10 individual distal fibers comprising polyester, nylon or silk of about 40 denier, and the proximal plurality of fibers comprises 8 to 10 individual proximal fibers comprising polyester, nylon or silk of about 40 denier; and wherein the member is about 0.25 mm to about 0.4 mm wide.
In a final aspect, the present invention is directed to an improvement in a vasoocclusive device adapted for introduction into a vessel of a human or veterinary patient and capable of occluding a flow in the vessel when introduced into the vessel, the device comprising: a member having a proximal end and a distal end spaced from the proximal end, the distal end of the member being introduced into the vessel before the proximal end of the member is introduced into the vessel; a distal plurality of fibers having an average distal fiber length, the distal plurality of fibers being associated with and extending away from the distal end of the member; and a proximal plurality of fibers having an average proximal fiber length, the proximal plurality of fibers being associated with and extending away from the proximal end of the member; the improvement wherein the average proximal fiber length is greater than the average distal fiber length.
In this final aspect of the invention, the designation of one end of the member in this general type of device as xe2x80x9cproximalxe2x80x9d and the other end of the member as xe2x80x9cdistalxe2x80x9d is arbitrary, and merely indicates that prior devices of this general type were in fact inserted into vessels one end before the other. This arbitrary designation does not mean that the proximal and distal ends of any prior device of this general type were distinguishable from one another in any way, nor does it mean that those skilled in the art have recognized any difference between the end of the device inserted first and the end of the device inserted second. Instead, the proximal and distal ends of the prior devices of this general type appear to be completely symmetric in their possession and arrangement of fibers, in direct contrast to the vasoocclusive device of the present invention. No contrary admission should be implied by the arbitrary designation herein of the ends of prior devices of this general type as xe2x80x9cproximalxe2x80x9d or xe2x80x9cdistal.xe2x80x9d
Again, as mentioned above, the vasoocclusive device of the present invention possesses several significant advantages. Most notably, the vasoocclusive device of the present invention enjoys superior and very reliable lodging in the targeted vessel in which it is inserted. The vasoocclusive device of the present invention can be used in vessels of very small diameter, in particular, in cranial vessels having a diameter below about 2.7 mm. Finally, the vasoocclusive device of the present invention can be introduced into a patient by injection with a fluid, rather than by being pushed with a rod or the like.